1. Field of the Invention
The invention is in the field of control systems for bidirectional counters and is particularly directed to a method and apparatus for using such a control system in connection with an optical correlator.
2. Description of the Prior Art
The invention concerns a method to obtain out-of-phase control signals forming an electrical rotating field for a bidirectional counter with the use of a measuring device having at least one optical device imaging an object, at least one grating structure, a drive to produce a periodic relative movement between the image of the object generated by the imaging optical device and the grating structure and a photoelectric receiver system coordinated with the grating structure to detect the movement of the object reproduced, in one of two opposing directions at least approximately parallel to said relative movement.
Optical correlators for the measurement of the relative movement of an object without special markings are known for example from German Offenlegungsschrift DT-OS 2 144 487, (equivalent to U.S. Pat. No. 3,989,378) incorporated herein by reference. Typically, the grating structure of the correlator is moved transversely to the optical axis of the imaging system, a reference signal is derived from this movement and the direction of motion of the object is dertermined by utilizing the reference signal being phase sensitively rectified. The signals obtained indicate the direction of the relative movement of the object of their frequency. They are suitable merely for the control of an indicator. Alternately, these signals may control two separate counters, each assigned to one direction of motion. In such a case, however, the instantaneous relative position of the object must be determined by forming the difference of the present count of the counters. This method is cumbersome and expensive.
It is therefore the object of the invention to provide a new method and apparatus which makes it possible to control a bidirectional counter interconnected specifically with an optical correlator. In the method, the complexity of the instrumental outlay provided between the correlator and the counter is maintained low to achieve an optimum, low cost system.